An engine built with your personal machine translation memories works better for you because it learned how to translate using your knowledge and style. That’s why you’re comfortable using it. Even it’s errors use your vocabulary with some of your style and overall, there’s less for you to correct.
But, your personalized translation engine does not work better for everyone. Other translators using your engine will feel differently about your engine’s translation. It’s natural for them to use different words in a different style. Likewise, if you were to use another translator’s personalized engine, you would likely feel less comfortable.